[FADCA] re: 802.11b/g Operations

Sat, 15 Feb 2003 07:34:20 -0500

Rich, Paul/All

Thanks for the real world feedback on the link estimates. That link
estimator URL does have a mechanism for adding in additional loss for trees.
We need to develop the "real world" loss fudge factors based on your
personal experiences. That would allow us neophyte microwavers to be able to
make more realistic estimates.

I think Paul is also right on with his suggestions of 3.3. and 5.5 GHz as
being better target frequencies. Locating or developing a good sources for a
2.4 to 3.3 or 5.5 Transverter/Amp/LNA would allow using the low cost WiFi
radios in those bands with higher power.

My initial effort is just to get familiar with setting up a wireless network
and then doing a little experimenting with external antennas.  The great
thing is the cost of the basic WiFi radios is reasonable enough to do this
even if in the end they are throw away.

Thanks for the help.

Rick

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Richard Garcia
Sent: Friday, February 14, 2003 1803 PM
To: [email protected]
Subject: RE: [FADCA] re: 802.11b/g Operations

I agree the link ranges are a bit optimistic. I work for a PCS provider so
1.9 Ghz is a daily routine for me and since I live  in somewhat rural
country I also get to play with 6 Ghz, I maintain part of a 12 hop Harris MW
system on 6 Ghz. Most PCS providers do not run more than 8-20 watts from a
site and that is out of the amp. Take into account about 200ft of 1 5/8
feedline and then a 18 DB antenna at about 150ft. Coverage in a ENGINEERED
system is about 3-4 mile radius, coverage on a clear channel is about double
that maybe a bit more. We often turn up new sites on a test channel at night
and have the site driven then turn it to a operational channel and drive it
again when it is in service.

Granted a point to point link will have directional antennas, not a little
handheld but the power is WAY lower than the average 16watts and I seriously
doubt that we will be lucky enough to get 2 points very high in a emergency
situation. Also remember that these are part 15 allocations, not a specific
band that only one carrier uses and has very accurate RF control over.
Co-Channel will be a very important case here to work with and the S/N will
reduce the range.

On 6 Ghz the average antenna height is between 100-140 ft. Usually diversity
with Primary at 140 and Diversity at 100 8ft Parabolic Dishes (ie Super High
Gain). We are talking $50K+ radios here and a 30 mile hop is marginal, so
much so we are relocating one to 15 miles. Granted 6 Ghz is much higher than
2.4 but the HSMM is looking at all bands above 900 Mhz, 5.8 is quite close.

I just got a commercial AP today I am going to play with it this weekend and
see how well it works without the BDA. I got to do some climbing to get the
amp/antenna so I don't know when that will be. But believe me paths are
going to be difficult to do unless you have some serious towers or mountians
to work with. City folk out there will have better luck since trees are not
a problem and a 12 story office or condo is easyer to get on after a
disaster in a pinch than dealing with large tower corporations. Case in
point one national tower company started requesting in November all tower
climbing crews to submit a few pounds of paperwork for climbing approval.
Requested is a Custom Designed Safety Handbook, certified training,
insurance documents and BANK STATEMENTS!! just to start. If you thought
tower access was bad last year hold on to the future!

My observations are seat of the pants granted but I deal with it all day
long on frequencies VERY close to what we are talking about, it just comes
second nature after so many years.

Rich K4GPS

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Paul J. Toth-NA4AR
Sent: Friday, February 14, 2003 4:02 PM
To: [email protected]
Subject: [FADCA] re: 802.11b/g Operations

Rick and all....

The HSMM is working on a number of different aspects of using DSSS
technology above 900 MHz for digital networking and communications.  The
hardware group is currently working on developing a recommended Hardware
List for Radio Amateurs to build their systems around.  The software group
is focusing on networking issues, applications and insuring the security and
integrity of the system while being in compliance with Part 97.  ?The
massive proliferation of 802.11b devices operating under Part 15 offers a
particularly interesting challenge for Amateur Radio that we seldom see in
any of our other bands.  There are also legal and regulatory issues to deal
with to make this effort whole.

Based on some experience in the commercial broadcast industry, I think the
range estimates Rick offered are a little optimistic, particuarly here in
Florida with all dense foliage and Summertime sub-tropical downpours.
Getting the antenna above the treeline is paramount for any microwave
signal.  "If you can see it, you can make the shot" was the philosophy we
lived by in my Broadcast News days.  I believe we will be lucky to achieve a
five mile (5 mi) footprint radius in many areas for local access (User to
Access Point).  This stuff just does not like trees!  It is also worth
noting the commercial WISPs are using cellular-like antenna arrays at their
Access Points rather than omni-directional antennas.  Better gain and
rejection of unwanted signals.  Point to point with two foot parabolic
dishes, I look for fifteen miles.  Using separate RX and TX antennas (which
is possible with some Access Points, like Linksys, may enhance the hop
distance a little.  The key on the Point-to-Point stuff will be to get the
antennas (and antenna-mounted ampifiers) up in the air between 170' and
300'.  The 5.7 GHz band may actually be better for backbone operations as
802.11a will support connectivity up to 54 MBps.

While there is still some room for Part 97 in the 2.4 GHz band, I believe
Amateur Radio's real future is in the 3.3 GHz band.  There is virtually no
Part 15 activity there at the present time to trashup the band.  If we can
stake a claim first, our ability to use some power (>100mW) may help deter
Part 15 activity.  The 2.4 GHz band is seeing so much activity in many
metropilitan areas and Californai it's hard to squeeze a signal in edgewise.
In fact, a 2.4 GHz Amateur Radio voice repeater in California was recently
turned off because it couldn't deal with the interference from a nearby
802.11b Access Point.  The ARRL is investigating this situation.

One other point worth noting.  In my presentation last Saturday at Orlando,
I noted a third potential area for development and activity...the 'Last
Mile" for EComm (or EmComm, if you prefer).  These high speed links offer us
the ability to do voice, video and data simultaneously, if we have the right
equipment on both ends of the link.  That means a Red Cross Field Operation
could have their telephones and computer data routed over the same link.
This is something to look at for supporting hospitals during a disaster.

Thanks to Doug-KN4YT for his comments this morning about ESATCOM.  Tying all
this together with satellite links is the ultimate high speed wireless
solution.  Until then, bring on the HF Pactor station that can route
messages to gateway stations.

73 de Paul-NA4AR
ARRL HSMM Working Group

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